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The digital logic shown in the figure satisfies the given state diagram when $Q1$ is connected to input $A$ of the XOR gate.

Suppose the XOR gate is replaced by an XNOR gate. Which one of the following options preserves the state

diagram?

- Input $A$ is connected to $\overline{Q2}$
- Input $A$ is connected to $Q2$
- Input $A$ is connected to $\overline{Q1}$ and $S$ is complemented
- Input $A$ is connected to $\overline{Q1}$

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Here the gate equation is given as $A\oplus S=Q_{1}\oplus S$

Now XOR gate changes to XNOR gate and still the equation remain same, i.e. $A\odot S=Q_{1}\odot S$

Now both equation will be equal when $Q_{1}\oplus S=Q_{1}\odot Sā=Q_{1}ā\odot S$

So, in place of $Q_{1}$ if we place $Q_{1}ā$ both will give similar output.

Now XOR gate changes to XNOR gate and still the equation remain same, i.e. $A\odot S=Q_{1}\odot S$

Now both equation will be equal when $Q_{1}\oplus S=Q_{1}\odot Sā=Q_{1}ā\odot S$

So, in place of $Q_{1}$ if we place $Q_{1}ā$ both will give similar output.